When drilling an oil or gas production well using a drill string, it is common to encounter static friction that limits advancement of the drill string into the bore being formed. In these instances it is known to be desirable to pulse the flow of drilling fluid pumped through the drill string to vibrate the drill and reduce the static friction so that deeper wells can be more readily produced. Examples of prior United States Patents relating to pulsing the flow of drilling fluid include U.S. Pat. No. 6,279,670 by Eddison et al; U.S. Pat. No. 4,819,745 by Walter; and U.S. Pat. No. 2,743,083 by Zublin.
In Zublin, U.S. Pat. No. 2,743,083, various embodiments are disclosed in which a rotating valve component is driven to rotate by suitable vanes coupled thereto or by the orientation of the flow passages therethrough. As the rotating valve component is directly driven by vanes coupled thereto, the amount of pulse capable is limited. Furthermore in some embodiments a bypass area is provided, however the bypass area is proportionally very large compared to the pulsing component so as to further limit the amount of pulsing possible.
Walter, U.S. Pat. No. 4,819,745, discloses a further example of a flow pulsing device in which the rotating component of the valve creating the pulses is driven by an impeller with vanes integrally associated therewith so that the overall structure of the integrated valve and impeller is very complex and can therefore have problems with reliability. The direct coupling of the impeller with the rotating valve component may also limit the amount of pulsing possible.
Eddison, U.S. Pat. No. 6,279,670, discloses another example of a flow pulsing apparatus in which a dedicated motor comprising a rotator rotating within a stator is required to be provided separate from the drilling motor just for driving the valve component. The overall assembly of a flow pulsing valve together with a motor operated solely for rotating the valve is a costly and complex structure to be installed in a drill string separate from the drilling motor.